Two years after a tsunami killed more than
2,000 people in a Papua
New Guinea village, scientists are offering the suggestion
that some of the largest tsunamis may be enhanced by underwater
landslides and slumps, in addition to the movement of the ocean
floor, because of an underwater earthquake.

"We've spent a lot of time looking
at the possible cause of the Papua New Guinea tsunami,"
said Eddie Bernard, director of NOAA's
Pacific Marine Environmental Laboratory in Seattle, Wash.,
which among other things, studies tsunamis. "There was just
something wrong with the timing and size which made us take a
look at other causes."

Earthquake-generated tsunamis travel at
known speeds. Sensors registered a magnitude 7 earthquake at
6:49 p.m. on July 17, 1998. However, by the accepted formula,
the wave that hit the north shore of the country was not only
about 10 minutes too late, it was also too big.

An international scientific team went quickly
to Papua New Guinea, located north of Australia, to begin to
find clues as to the tsunami's origin. Communications are often
very basic to non-existent in PNG, and it was critical to get
eyewitness accounts and collect evidence in place before survivors
relocated or material was removed by storms or scavengers.

Despite conflicting information about the
wave's arrival time, the team was able to determine that the
first wave hit shore a few minutes after 7 p.m. It is often the
second tsunami wave that does the most damage, as curious spectators,
believing that the worst is over, wade out into the receding
water or climb down from a safe spot on high ground,

Noting many landslides on shore, the survey
team suggested that the tsunami may have been triggered by an
offshore slide, which would account for the timing delay and
the larger-than-expected wall of water. A marine survey consisting
of multi-beam bathymetric surveys and visual examinations with
manned submersibles was conducted that found evidence of a slump,
which starts and stops, and reacts to shifts in the ocean floor.
Landslides, on the other hand, accelerate and just keep on going.

Earlier this year, researchers from the
United States Geological Survey found evidence of a similar land
formation off the southern California coast. A team from the
Woods Hole Oceanographic Institution also discovered faults in
the ocean floor on the east coast, an area not usually associated
with tsunamis, most likely caused by eruptions of gas trapped
under layers of sediment.

"These discoveries are drawing our
attention to other causes of tsunamis, besides the traditional
tectonic earthquake," said Bernard. "The more we learn
about possible causes, the better we can know when to issue warnings."

There are two U.S.-operated tsunami warning
centers, one each in Alaska and Hawaii and run by NOAA's
National Weather Service. These two centers use seismometers
to detect the occurrence of earthquakes within minutes of the
start of an earthquake. They cannot, however, detect underwater
landslides or slumps with these instruments.

A series of buoys anchored along the Pacific
coast from Alaska to Monterey, Calif., can detect the presence
of a tsunami. So even if a slump or landslide generates a tsunami,
tsunami detectors exist to warn people of its dangers.

As with any natural hazard, the more informed
the public is, the better are the chances for their survival.
For instance, after the 1998 PNG tsunami, a team went to Vanuatu,
a group of islands in the Pacific, and showed videos of earthquakes,
tsunamis, and volcanoes to villagers. When a tsunami stuck there
last December, only three people died. According to the research
laboratory team, the others remembered the lessons of the video
and headed for high ground when the earth began to shake and
the water began to recede.